U.S. patent application number 15/258131 was filed with the patent office on 2017-03-30 for slurry for thermal spraying.
This patent application is currently assigned to FUJIMI INCORPORATED. The applicant listed for this patent is FUJIMI INCORPORATED. Invention is credited to Hiroyuki IBE, Takaya MASUDA, Kazuyuki TSUZUKI.
Application Number | 20170088928 15/258131 |
Document ID | / |
Family ID | 58408535 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170088928 |
Kind Code |
A1 |
IBE; Hiroyuki ; et
al. |
March 30, 2017 |
SLURRY FOR THERMAL SPRAYING
Abstract
To provide a slurry for thermal spraying capable of forming a
favorable sprayed coating. The present invention provides a slurry
for thermal spraying including spray particles including at least
one material selected from the group consisting of ceramics,
inorganic compounds, cermets, and metals and a dispersion medium.
Here, the spray particles have an average particle size of 0.01
.mu.m or more and 10 .mu.m or less and are contained in the slurry
for thermal spraying at a proportion of 10% by mass or more and 70%
by mass or less. In the slurry for thermal spraying, the spray
particles have a zeta potential of -200 mV or more and 200 mV or
less.
Inventors: |
IBE; Hiroyuki; (Aichi,
JP) ; TSUZUKI; Kazuyuki; (Aichi, JP) ; MASUDA;
Takaya; (Aichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIMI INCORPORATED |
Kiyosu-shi |
|
JP |
|
|
Assignee: |
FUJIMI INCORPORATED
Kiyosu-shi
JP
|
Family ID: |
58408535 |
Appl. No.: |
15/258131 |
Filed: |
September 7, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 7/61 20180101; C09D
7/69 20180101; C09D 5/024 20130101; C23C 4/04 20130101; C23C 4/134
20160101; C09D 1/00 20130101; C23C 4/129 20160101 |
International
Class: |
C23C 4/04 20060101
C23C004/04; C09D 7/12 20060101 C09D007/12; C09D 5/02 20060101
C09D005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2015 |
JP |
2015-188834 |
Claims
1. A slurry for thermal spraying, the slurry comprising: spray
particles including at least one material selected from the group
consisting of ceramics, inorganic compounds, cermets, and metals;
and a dispersion medium, wherein the spray particles have an
average particle size of 0.01 .mu.m or more and 10 .mu.m or less,
the spray particles are contained in the slurry for thermal
spraying at a proportion of 10% by mass or more and 70% by mass or
less, and in the slurry for thermal spraying, the spray particles
have a zeta potential of -200 mV or more and 200 mV or less.
2. The slurry for thermal spraying according to claim 1, further
comprising a dispersant.
3. The slurry for thermal spraying according to claim 1, wherein at
least some of the spray particles include an yttrium
oxyfluoride.
4. The slurry for thermal spraying according to claim 1, wherein at
least some of the spray particles include a rare earth halide.
5. The slurry for thermal spraying according to claim 1, wherein
the slurry for thermal spraying has a viscosity of 1,000 mPas or
less.
6. The slurry for thermal spraying according to claim 1, wherein
the dispersion medium is an aqueous dispersion medium.
7. The slurry for thermal spraying according to claim 1, wherein
the dispersion medium is a nonaqueous dispersion medium.
8. A sprayed coating including a thermal spray product of the
slurry for thermal spraying according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The present invention relates to a slurry for thermal
spraying including spray particles.
[0003] Description of the Related Art
[0004] Techniques of covering the surfaces of substrates with
various materials to impart novel functions have been used in
various fields. As one of the surface covering techniques, a
thermal spraying method is known, for example. In the method, spray
particles including a ceramic, a cermet, a metal, or a similar
material are softened or melted by combustion or electric energy,
and are sprayed to the surface of a substrate, thereby giving a
sprayed coating including such a material (for example, see Patent
Document 1).
[0005] In the thermal spraying, spray particles as a coating
material are typically fed in a powder form to a thermal spraying
apparatus. In recent years, spray particles are dispersed in a
dispersion medium and fed in a slurry (including a suspension) form
to a thermal spraying apparatus. As a conventional technique
relating to the slurry for thermal spraying, Patent Document 2 is
exemplified.
CITATION LIST
Patent Literature
[0006] PTL 1: JP 2014-240511 A
[0007] PTL 2: JP 2010-150617 A
SUMMARY OF THE INVENTION
[0008] A slurry for thermal spraying in which spray particles are
dispersed in a dispersion medium cannot maintain the dispersion
state of the spray particles during storage of the slurry due to a
difference in specific gravity of materials thereof or particle
sizes, and the spray particles may sediment to form precipitates in
some cases. Spray particles that have precipitated have no
flowability, and thus a slurry for thermal spraying that is likely
to generate precipitates is unsuitable as the material for thermal
spraying. In addition, when a larger amount of spray particles
precipitate, the feed amount of a slurry for thermal spraying may
be reduced, or a slurry may cause clogging in a feeding device.
[0009] In such circumstances, the inventors of the present
invention have repeatedly conducted various studies, and
consequently have found that even a slurry for thermal spraying
capable of generating precipitates can form a high quality sprayed
coating and is suitable as a material for thermal spraying when
spray particles can be satisfactory dispersed in a dispersion
medium. The present invention is completed on the basis of the
above findings and intends to provide a slurry for thermal spraying
capable of forming a favorable sprayed coating. The present
invention further intends to provide a sprayed coating formed by
using the slurry for thermal spraying.
[0010] The present invention provides a slurry for thermal spraying
having the following characteristics to solve the above problems.
The slurry for thermal spraying includes spray particles including
at least one material selected from the group consisting of
ceramics, inorganic compounds, cermets, and metals and a dispersion
medium. Here, the spray particles have an average particle size of
0.01 .mu.m or more and 10 .mu.m or less, and are contained in the
slurry for thermal spraying at a proportion of 10% by mass or more
and 70% by mass or less. In the slurry for thermal spraying, the
spray particles have a zeta potential of -200 mV or more and 200 mV
or less.
[0011] When having such a structure, a slurry for thermal spraying
allows the spray particles to be in a good dispersion state, and
this can improve feeding performance when the slurry is fed to a
thermal spraying apparatus. Accordingly, a slurry for thermal
spraying that can be stably fed in appropriate dispersion and flow
conditions to a thermal spraying apparatus can be achieved.
Consequently, a slurry for thermal spraying capable of forming a
uniform and dense sprayed coating can be provided.
[0012] In a preferred aspect of the slurry for thermal spraying
disclosed here, the slurry further includes a dispersant. When
having such a structure, a slurry for thermal spraying in which the
dispersion stability of the spray particles is more improved is
provided.
[0013] In a preferred aspect of the slurry for thermal spraying
disclosed here, at least some of the spray particles include an
yttrium oxyfluoride. When having such a structure, a slurry for
thermal spraying enables the formation of a sprayed coating having
excellent plasma erosion resistance.
[0014] In a preferred aspect of the slurry for thermal spraying
disclosed here, at least some of the spray particles include a rare
earth halide. When the slurry for thermal spraying having such a
structure is thermally sprayed, a sprayed coating having novel
characteristics due to the rare earth halide can be formed. In the
present description, the "average particle size" of spray particles
is an average particle size (sphere equivalent diameter) calculated
on the basis of specific surface area, for spray particles having
an average particle size of less than 1 .mu.m. The average particle
size D is a value calculated in accordance with the equation:
D=6/(.rho.S) where
[0015] S is the specific surface area of spray particles and p is
the density of the material constituting spray particles. For
example, when the spray particles are yttria (yttrium oxide:
Y.sub.2O.sub.3), the average particle size can be calculated where
the density .rho. is 5.01 g/cm.sup.3. The specific surface area of
spray particles can be a value determined by a gas adsorption
method, for example, and can be measured in accordance with JIS Z
8830: 2013 (1509277: 2010)
[0016] "Determination of the specific surface area of powders
(solids) by gas adsorption". For example, the specific surface area
of spray particles can be determined by using a surface area
analyzer, trade name "FlowSorb II 2300" manufactured by
Micromeritics. For spray particles having an average particle size
of 1 .mu.m or more, the particle size at an integrated value of 50%
in volumetric particle size distribution (50% cumulative particle
size) determined with a particle size distribution analyzer based
on the laser scattering/diffraction method is used as the "average
particle size".
[0017] In a preferred aspect of the slurry for thermal spraying
disclosed here, the slurry for thermal spraying has a viscosity of
1,000 mPas or less. When having such a structure, a slurry for
thermal spraying in which spray particles are prevented from
sedimenting and the flow state is appropriately conditioned is
provided.
[0018] In the present description, the viscosity of a slurry for
thermal spraying is a viscosity at room temperature (25.degree. C.)
determined by using a rotational viscometer. Such a viscosity can
be a value determined by using a Brookfield viscometer (for
example, manufactured by Rion, Viscotester VT-03F), for
example.
[0019] In a preferred aspect of the slurry for thermal spraying
disclosed here, the dispersion medium is an aqueous dispersion
medium. When having such a structure, a material for thermal
spraying that have a lower environmental load is provided because
the amount of organic solvents used is reduced or the use is
unnecessary. In addition, when an aqueous dispersion medium is
used, a resulting sprayed coating has a smoother surface and a
lower surface roughness as compared with the case using a
nonaqueous dispersion medium is used, and this is advantageous.
[0020] In a preferred aspect of the slurry for thermal spraying
disclosed here, the dispersion medium is a nonaqueous dispersion
medium. When having such a structure, a material for thermal
spraying that can be thermally sprayed at a lower temperature is
provided. When a nonaqueous dispersion medium is used, a resulting
sprayed coating has a lower porosity as compared with the case
using an aqueous dispersion medium, and this is advantageous.
[0021] In another aspect, the present invention provides a sprayed
coating including a thermal spray product of any of the above
slurries for thermal spraying. The sprayed coating can be formed by
thermal spraying at high efficiency by using particles for thermal
spraying having a comparatively small average particle size, for
example. Accordingly, the sprayed coating can be formed as a dense
sprayed coating having high adhesiveness and coating strength.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Preferred embodiments of the present invention will now be
described. Matters not specifically mentioned in the present
description but required for carrying out the present invention can
be understood by a person skilled in the art on the basis of
teachings on the implementation of the invention described in the
present description and common general knowledge at the time of the
patent application. The present invention can be carried out on the
basis of the contents disclosed in the present description and
common general knowledge in the field.
[0023] [Slurry for Thermal Spraying]
[0024] The slurry for thermal spraying disclosed here essentially
includes spray particles including at least one material selected
from the group consisting of ceramics, inorganic compounds,
cermets, and metals and a dispersion medium. In the slurry for
thermal spraying, the zeta potential of the spray particles that
are dispersed in the dispersion medium is -200 mV or more and 200
mV or less. In other words, the spray particles in the slurry for
thermal spraying are so prepared as to have an absolute zeta
potential of 200 mV or less. The zeta potential is preferably -180
mV or more and 180 mV or less, more preferably -150 mV or more and
150 mV or less, and even more preferably, for example, 0 mV or more
and 150 mV or less.
[0025] It is generally believed that when a dispersion system
including particles and a dispersion medium has a larger absolute
zeta potential, the dispersibility of the particles is higher, thus
the particles are unlikely to agglomerate, and the particles are
dispersed in the liquid at a uniform concentration. In other words,
repulsive force is generated between the respective particles, and
the dispersion state is maintained in a primary particle state.
Thus, the zeta potential of particles in a dispersion system is set
to several hundreds mV or more in many cases.
[0026] In contrast, in the dispersion system of a slurry for
thermal spraying including spray particles of the above material
and a dispersion medium, the spray particles can be difficult to
maintain a dispersion state. When the spray particles include a
ceramic, an inorganic compound, a cermet, a metal, or a similar
material having a larger specific gravity than those of resin
materials and the like, the tendency becomes much higher. In the
technique disclosed here, the inventors have found that when spray
particles agglomerate to some extent, but the particles in a
secondary particle state do not largely repel each other or
agglomerate, and the repulsive force is cancelled by the attractive
force or the difference of the forces is small, the spray particles
are in a state suitable for thermal spraying. The zeta potential of
the spray particles in the slurry for thermal spraying
(hereinafter, also simply called "zeta potential") is therefore
specified to be in a range from -200 mV to 200 mV. In the
dispersion system of the slurry for thermal spraying in such a
condition, a stable dispersion state can be maintained in a flow
state even when spray particles precipitate or agglomerate. In the
dispersion state, the spray particles may agglomerate to form
secondary particles.
[0027] The zeta potential of spray particles is used as an index
representing flowability (mobility) of the spray particles in the
slurry for thermal spraying disclosed here. Hence, in measurement
of the zeta potential, a value determined without any pretreatment
such as dilution of a slurry for thermal spraying to be measured
can be adopted. The measurement method of the zeta potential can be
a known measurement technique such as a microscope electrophoresis
method, a rotational diffraction grating method, a laser doppler
electrophoresis method, an ultrasonic vibration potential method,
and an electrokinetic sonic amplitude method. Of them, the
ultrasonic vibration potential method that can determine the zeta
potential of spray particles in a high-concentration thermal
spraying slurry can be preferably adopted because ultrasonic waves
are applied to vibrate the spray particles in a thermal spraying
slurry and the zeta potential is measured.
[0028] (Particles for Thermal Spraying)
[0029] The spray particles can include spray particles including at
least one material selected from the group consisting of ceramics,
inorganic compounds, cermets, and metals.
[0030] The ceramic is not limited to particular ceramics. The
ceramic can be exemplified by oxide ceramics including various
metal oxides, carbide ceramics including of metal carbides, nitride
ceramics including metal nitrides, and nonoxide ceramics including
nonoxides such as metal borides, metal fluorides, metal hydroxides,
metal carbonates, and metal phosphates.
[0031] The oxide ceramic is not limited to particular ceramics, and
various metal oxides can be used. Examples of the metallic element
constituting such an oxide ceramic include metalloid elements such
as B, Si, Ge, Sb, and Bi; typical metal elements such as Na, Mg,
Ca, Sr, Ba, Zn, Al, Ga, In, Sn, Pb, and P; transition metal
elements such as Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe,
Co, Ni, Cu, Ag, and Au; and lanthanoid elements such as La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tu, Yb, and Lu. These elements
can be used singly or in combination of two or more of them.
Specifically preferred are one or more elements selected from Mg,
Y, Ti, Zr, Cr, Mn, Fe, Zn, Al, and Er. The oxide ceramic disclosed
here also preferably contains, in addition to the above metallic
element, a halogen element such as F, Cl, Br, and I.
[0032] More specifically, examples of the oxide ceramic include
alumina, zirconia, yttria, chromia, titania, cobaltite, magnesia,
silica, calcia, ceria, ferrite, spinel, zircon, forsterite,
steatite, cordierite, mullite, nickel oxide, silver oxide, copper
oxide, zinc oxide, gallium oxide, strontium oxide, scandium oxide,
samarium oxide, bismuth oxide, lanthanum oxide, lutetium oxide,
hafnium oxide, vanadium oxide, niobium oxide, tungsten oxide,
manganese oxide, tantalum oxide, terbium oxide, europium oxide,
neodymium oxide, tin oxide, antimony oxide, antimony-containing tin
oxide, indium oxide, barium titanate, lead titanate, lead zirconate
titanate, Mn-Zn ferrite, Ni-Zn ferrite, sialon, tin-containing
indium oxide, zirconium oxide aluminate, zirconium oxide silicate,
hafnium oxide aluminate, hafnium oxide silicate, titanium oxide
silicate, lanthanum oxide silicate, lanthanum oxide aluminate,
yttrium oxide silicate, titanium oxide silicate, tantalum oxide
silicate, yttrium oxyfluoride, yttrium oxychloride, yttrium
oxybromide, and yttrium oxyiodide.
[0033] Examples of the nonoxide ceramic include carbide ceramics
such as tungsten carbide, chromium carbide, niobium carbide,
vanadium carbide, tantalum carbide, titanium carbide, zirconium
carbide, hafnium carbide, silicon carbide, and boron carbide;
nitride ceramics such as silicon nitride and aluminum nitride;
boride ceramics such as hafnium boride, zirconium boride, tantalum
boride, and titanium boride; hydroxide ceramics such as
hydroxyapatite; and phosphoric acid ceramics such as calcium
phosphate.
[0034] The inorganic compound is not limited to particular
compounds, and can be exemplified by semiconductors such as
silicon, and particles (optionally powders) of inorganic compounds
such as various carbides, nitrides, and borides. The inorganic
compound may be a crystalline compound or an amorphous compound.
Specifically preferred examples of the inorganic compound include
halides of rare earth elements.
[0035] In the rare earth halide, the rare earth element (RE) is not
limited to particular rare earth elements and can be appropriately
selected from scandium, yttrium, and lanthanoid elements.
Specifically, the rare earth element is exemplified by scandium
(Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr),
neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),
gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),
erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). These
elements may be used singly or in combination of two or more of
them. Preferred examples include Y, La, Gd, Tb, Eu, Yb, Dy, and Ce
from the viewpoint of improving the plasma erosion resistance or
prices, for example. These rare earth elements may be contained
singly or in combination of two or more of them.
[0036] The halogen element (X) is also not limited to particular
elements and may be any element belonging to Group 17 in the
periodic table. Specifically, halogen elements such as fluorine
(F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At) may
be used singly or in combination of two or more of them. The
halogen element is preferably F, Cl, or Br. These halogen elements
may be contained singly or in combination of two or more of them.
As such a rare earth halide, fluorides of various rare earth
elements, typified by yttrium fluoride (YF.sub.3), are exemplified
as preferred examples.
[0037] The metal is not limited to particular metals and is
exemplified by various elemental metals exemplified as the
constituent elements of the above ceramics and alloys including
such an element and one or more other elements. The elemental metal
is typically exemplified by nickel, copper, aluminum, iron,
chromium, niobium, molybdenum, tin, and lead. The alloy is
exemplified by nickel-based alloys, chromium-based alloys,
copper-based alloys, and steels. Here, the alloy encompasses
substances that include the above metallic element and one or more
other elements and exhibit metallic characteristics, and may be any
of solid solutions, intermetallic compounds, and mixtures of them
in terms of mixing manner.
[0038] The cermet is not limited to particular cermets, and can be
general composite materials prepared by bonding ceramic particles
with a metal matrix. The cermet can be a composite of the above
exemplified ceramic and the metal. More specifically, the cermet is
typically exemplified by composites (cermets) of titanium compound
ceramics such as titanium carbide (TiC) and titanium carbonitride
(TiCN), carbide ceramics such as tungsten carbide (WC) and chromium
carbide (CrC), and oxide ceramics such as alumina (Al.sub.2O.sub.3)
with metals such as iron (Fe), chromium (Cr), molybdenum (Mo), and
nickel (Ni). Such a cermet can be prepared by burning intended
ceramic particles and metal particles in an appropriate atmosphere,
for example.
[0039] The spray particles disclosed here preferably include spray
particles including specifically at least an yttrium oxyfluoride
among the above ceramics, inorganic compounds, cermets, and metals.
The yttrium oxyfluoride can be a compound containing at least
yttrium (Y), oxygen (O), and fluorine (F) as constituent elements.
The ratio of yttrium (Y), oxygen (O), and fluorine (F) constituting
the yttrium oxyfluoride is not limited to particular values.
[0040] For example, the molar ratio of fluorine to oxygen (F/O) is
not limited to particular values. As a preferred example, the molar
ratio (F/O) can be 1, for example, and is preferably more than 1.
Specifically, for example, the molar ratio is preferably 1.2 or
more, more preferably 1.3 or more, and particularly preferably 1.4
or more. The upper limit of the molar ratio (F/O) is not limited to
particular values and can be 3 or less, for example. As a more
preferred example, the molar ratio of fluorine to oxygen (F/O) is,
for example, 1.3 or more and 1.53 or less (for example, 1.4 or more
and 1.52 or less), 1.55 or more and 1.68 or less (for example, 1.58
or more and 1.65 or less), or 1.7 or more and 1.8 or less (for
example, 1.72 or more and 1.78 or less). In such a condition,
thermal stability can be improved at the time of thermal spraying,
and thus such a ratio is preferred. When spray particles have such
a higher ratio of fluorine to oxygen, a sprayed coating as a
thermal spray product of the slurry for thermal spraying can obtain
excellent erosion resistance against halogen plasma, and thus such
spray particles are preferred.
[0041] In the technique disclosed here, the halogen plasma is
typically a plasma generated by using a plasma generating gas
including a halogen-containing gas (halogenated compound gas).
Specific examples of the halogen-containing gas include
fluorine-containing gases used, for example, in a dry etching step
at the time of production of semiconductor substrates, such as
SF.sub.6, CF.sub.4, CHF.sub.3, ClF.sub.3, and HF;
chlorine-containing gases such as Cl.sub.2, BCl.sub.3, and HCl;
[0042] bromine-containing gases such as HBr; and iodine-containing
gases such as HI. These gases can be used singly or as a mixture of
two or more of them, and the plasma generated by using such a gas
can be typically exemplified. Such a gas may be a mixed gas with an
inert gas such as argon (Ar).
[0043] The molar ratio of yttrium to oxygen (Y/O) is not limited to
particular values. As a preferred example, the molar ratio (Y/O)
can be 1 and is preferably more than 1. Specifically, for example,
the molar ratio is preferably 1.05 or more, more preferably 1.1 or
more, and particularly preferably 1.15 or more. The upper limit of
the molar ratio (Y/O) is not limited to particular values and can
be 1.5 or less, for example. As a more preferred example, the molar
ratio of yttrium to oxygen (Y/O) is, for example, 1.1 or more and
1.18 or less (for example, 1.12 or more and 1.17 or less), 1.18 or
more and 1.22 or less (for example, 1.19 or more and 1.21 or less),
or 1.22 or more and 1.3 or less (for example, 1.23 or more and 1.27
or less).
[0044] In such a condition, thermal stability can be improved at
the time of thermal spraying, and thus such a ratio is preferred.
When a slurry for thermal spraying containing spray particles
having such a small ratio of an oxygen element to yttrium is
thermally sprayed, the spray particles can be prevented from
undergoing oxidative decomposition, and thus such spray particles
are preferred. For example, in a sprayed coating as a thermal spray
product of the slurry for thermal spraying, the formation of
yttrium oxides (for example, Y.sub.2O.sub.3) by oxidation of an
yttrium component can be suppressed, and thus such spray particles
are preferred.
[0045] More specifically, the yttrium oxyfluoride may be a compound
represented by YOF as the chemical composition where the ratio of
yttrium, oxygen, and fluorine is 1:1:1. The yttrium oxyfluoride may
also be Y.sub.5O.sub.4F.sub.7, Y.sub.6O.sub.5F.sub.8,
Y.sub.7O.sub.6F.sub.9, Y.sub.17O.sub.14F.sub.23, and the like that
are comparatively, thermodynamically stable and are represented by
the general formula: Y.sub.1O.sub.1-nF.sub.1+2n (where n satisfies
0.12.ltoreq.n.ltoreq.0.22, for example). In particular,
Y.sub.5O.sub.4F.sub.7, Y.sub.5O.sub.5F.sub.8,
Y.sub.7O.sub.6F.sub.9, and the like in which the molar ratios (Y/O)
and (F/O) are within the above preferred ranges can form a denser
sprayed coating having higher hardness and having excellent plasma
erosion resistance against halogen gas plasma, and thus are
preferred. Such an yttrium oxyfluoride may include of a monophase
of any one of the compounds or may include a mixed phase, a solid
solution, or a compound of two or more compounds in combination or
a mixture of them.
[0046] The slurry for thermal spraying disclosed here may contain
spray particles include other ceramics, inorganic compounds,
metals, or cermets in addition to the spray particles including the
yttrium oxyfluoride. However, for example, in the slurry for
thermal spraying used for forming a sprayed coating having
excellent plasma erosion resistance, the spray particles preferably
contain a larger amount of the yttrium oxyfluoride. The yttrium
oxyhalide is preferably contained in the spray particles at a high
proportion of 77% by mass or more. The yttrium oxyfluoride has much
higher plasma erosion resistance than that of yttria
(Y.sub.2O.sub.3) that has been known as a material having high
plasma erosion resistance. When contained even in a small amount,
the yttrium oxyfluoride greatly improves the plasma erosion
resistance. When contained in such a large amount as described
above, the yttrium oxyfluoride can achieve extremely excellent
plasma resistance. Such a condition is therefore preferred. The
proportion of the yttrium oxyfluoride is more preferably 80% by
mass or more (more than 80% by mass), even more preferably 85% by
mass or more (more than 85% by mass), further preferably 90% by
mass or more (more than 90% by mass), and further more preferably
95% by mass or more (more than 95% by mass). For example, the
proportion is particularly preferably, substantially 100% by mass
(100% except unavoidable impurities). When containing the yttrium
oxyfluoride at such a high proportion, the spray particles can
contain other substances that are likely to become particles.
[0047] When spray particles contain the yttrium oxyfluoride, the
whole spray particles can include of the yttrium oxyfluoride in a
preferred embodiment. However, when containing an yttrium
oxyfluoride having a composition comparatively susceptible to
oxidation (for example, Y.sub.1O.sub.1F.sub.1), the spray particles
preferably contain a halide of a rare earth element at a proportion
of 23% by mass or less, for example. The rare earth halide
contained in spray particles can be oxidized during thermal
spraying to form an oxide of the rare earth element in a sprayed
coating. For example, yttrium fluoride can be oxidized during
thermal spraying to form yttrium oxide in a sprayed coating. The
yttrium oxide can become the generation source of particles in an
environment exposed to halogen plasma. Meanwhile, an yttrium
oxyfluoride (for example, Y.sub.1O.sub.1F.sub.1) can also be
oxidized during thermal spraying to form yttrium oxide in a sprayed
coating. When the yttrium oxyfluoride is present together with a
small amount of a rare earth halide, the oxidation of the yttrium
oxyfluoride can be suppressed by the rare earth halide, and thus
the coexistence is preferred. However, an excess proportion of a
rare earth halide results in an increase of the particle source as
described above, and thus a proportion of more than 23% by mass is
unfavorable because the plasma erosion resistance is deteriorated.
From such a viewpoint, the proportion of the rare earth halide is
preferably 20% by mass or less, more preferably 15% by mass or
less, even more preferably 10% by mass or less, and, for example,
preferably 5% by mass or less. In a more preferred embodiment of
the material for thermal spraying disclosed here, substantially no
rare earth halide (for example, yttrium fluoride) can be
contained.
[0048] Spray particles including yttrium oxide (Y.sub.2O.sub.3)
form a white sprayed coating and can be a preferred material in
order to form a sprayed coating having environmental barrier
properties or erosion resistance against typical plasma. Spray
particles can also be so constituted as to contain substantially no
oxide of yttrium (yttrium oxide: Y.sub.2O.sub.3) component so that
a sprayed coating as a thermal spray product can achieve plasma
resistance at a higher level. For example, the slurry for thermal
spraying containing spray particles including the yttrium
oxyfluoride preferably contains no spray particles including
yttrium oxide. Yttrium oxide included in spray particles can remain
as yttrium oxide in a sprayed coating formed by thermal spraying.
The yttrium oxide has extremely low plasma resistance as compared
with yttrium oxyfluorides and rare earth halides, for example, as
described above. Hence, an area containing yttrium oxide is likely
to form a brittle altered layer when exposed to a plasma
environment, and the altered layer is likely to generate extremely
fine particles and to be released. The fine particles may deposit
on a semiconductor substrate. On this account, in the slurry for
thermal spraying disclosed here, yttrium oxide, which can become a
particle source, is preferably excluded.
[0049] In the present description, "containing substantially no
component" means that the proportion of the component (here,
yttrium oxide) is 5% by mass or less, preferably 3% by mass or
less, and, for example, 1% by mass or less. Such a structure can be
ascertained by that diffraction peaks based on the component are
not detected in X-ray diffraction analysis of the spray particles,
for example.
[0050] When spray particles contain multiple (for example, a, where
a is a natural number and a .gtoreq.2) compositions of yttrium
oxyfluorides and/or rare earth halides, the proportion of each
composition can be calculated by the following procedure. First,
the compositions of compounds constituting spray particles are
identified by X-ray diffraction analysis. In this analysis, valence
numbers (element ratio) of the yttrium oxyfluoride are needed to be
identified.
[0051] For example, when a single type of yttrium oxyfluoride is
present and the remaining is YF.sub.3 in a material for thermal
spraying, the oxygen content in the material for thermal spraying
is determined with, for example, an oxygen/nitrogen/hydrogen
analyzer (for example, manufactured by LECO, ONH836). From the
obtained oxygen concentration, the content of the yttrium
oxyfluoride can be quantitatively determined.
[0052] When two or more types of yttrium oxyfluorides are present
or an oxygen-containing compound such as yttrium oxide is mixed,
the proportion of each compound can be quantitatively determined by
a calibration curve method, for example. Specifically, several
samples are prepared by changing the proportion of each compound,
and each sample is subjected to X-ray diffraction analysis. A
calibration curve indicating the relation between a main peak
intensity and the content of a corresponding compound is prepared.
On the basis of the calibration curve, the content is
quantitatively determined from the main peak intensities of yttrium
oxyfluorides in XRD of a material for thermal spraying to be
measured.
[0053] As for the molar ratio (F/O) and the molar ratio (Y/O) in
the above yttrium oxyfluoride, the molar ratio (Fa/Oa) and the
molar ratio (Ya/Oa) of each composition are calculated, then the
molar ratio (Fa/Oa) and the molar ratio (Ya/Oa) are multiplied by
the abundance ratio of the corresponding composition, and the
results are summed up (the weighted sum is calculated), thereby
enabling the calculation of the molar ratio (F/O) and the molar
ratio (Y/O) of all the yttrium oxyhalides in spray particles.
[0054] The materials constituting the spray particles may include
other elements in addition to the above exemplified elements, in
order to improve functionalities, for example. Each of the ceramic,
the inorganic compound, the cermet, and the metal may be a mixture
or a composite including two or more compositions. Two or more of
the ceramic, the inorganic compound, the cermet, and the metal may
be mixed.
[0055] The spray particles may be any particles that have an
average particle size of about 30 .mu.m or less, and the lower
limit of the average particle size is also not limited to
particular values. Here, spray particles having a comparatively
small average particle size are preferably used in the slurry for
thermal spraying disclosed here because the improvement effect of
the feeding performance is obvious. From such a viewpoint, the
average particle size of the spray particles can be, for example,
10 .mu.m or less and can be preferably 8 .mu.m or less, more
preferably 6 .mu.m or less, and, for example, 5 .mu.m or less. The
lower limit of the average particle size can be, for example, 0.01
.mu.m or more and can be preferably 0.05 .mu.m or more, more
preferably 0.1 .mu.m or more, and, for example, 0.5 .mu.m or more,
in consideration of the viscosity or flowability of the slurry for
thermal spraying. When the average particle size is about 1 .mu.m
or more, the viscosity of the slurry for thermal spraying can be
prevented from excessively increasing, and thus such a condition is
preferred.
[0056] For example, when fine spray particles having an average
particle size of about 10 .mu.m or less are used as the thermal
spraying material, the specific surface area is increased, and
accordingly the flowability can be reduced, typically. Such a
thermal spraying material thus has poor feeding performance to a
thermal spraying apparatus, and the thermal spraying material
adheres to a feed line, for example, and is difficult to feed to a
thermal spraying apparatus. Hence, the coating formability may
deteriorate. In addition, such a thermal spraying material has a
small mass, thus can be hit by a thermal spraying flame or a jet
stream, and can be difficult to fly appropriately. In contrast, in
the slurry for thermal spraying disclosed here, for example, spray
particles even having an average particle size of 10 .mu.m or less
are prepared as a slurry in consideration of feeding performance to
a thermal spraying apparatus. Thus, the slurry is prevented from
adhering to a feed line or the like and can maintain high coating
formability. In addition, the particles are fed to a flame or a jet
stream in a slurry state, thus are not hit by the flame or the jet,
and can fly with the stream. Moreover, a dispersion medium is
removed during flying. Hence, the thermal spraying efficiency is
maintained at a higher level, and a sprayed coating can be
formed.
[0057] (Dispersion Medium)
[0058] The slurry for thermal spraying disclosed here can include
an aqueous dispersion medium or a nonaqueous dispersion medium.
[0059] Examples of the aqueous dispersion medium include water and
mixtures of water and a water-soluble organic solvent (mixed
aqueous solutions). As the water, tap water, ion-exchanged water
(deionized water), distilled water, and pure water can be used, for
example. As the organic solvent except water constituting the mixed
aqueous solution, one or more of organic solvents that are
homogeneously miscible with water (for example, lower alcohols and
lower ketones having 1 to 4 carbon atoms) can be appropriately
selected and used. As the aqueous solvent, for example, a mixed
aqueous solution containing water at 80% by mass or more (more
preferably 90% by mass or more, even more preferably 95% by mass or
more) in the aqueous solvent is preferably used. Specifically
preferred examples include aqueous solvents substantially including
water (for example, tap water, distilled water, pure water, and
purified water).
[0060] As the nonaqueous solvent, organic solvents containing no
water are typically exemplified. Such an organic solvent is not
limited to particular solvents, and is exemplified by alcohols such
as methanol, ethanol, n-propyl alcohol, and isopropyl alcohol; and
organic solvents such as toluene, hexane, and kerosene. These
solvents can be used singly or in combination of two or more of
them.
[0061] The type and the composition of the dispersion medium to be
used can be appropriately selected according to a thermal spray
method of the slurry for thermal spraying, for example. In other
words, for example, when the slurry for thermal spraying is
thermally sprayed by a high velocity flame spraying method, any of
the aqueous solvents and the nonaqueous solvents can be used. When
an aqueous dispersion medium is used, the surface roughness of a
resulting sprayed coating is improved (a smoother surface) as
compared with the case using a nonaqueous dispersion medium, and
this is advantageous. When a nonaqueous dispersion medium is used,
a resulting sprayed coating has a lower porosity as compared with
the case using an aqueous dispersion medium, and this is
advantageous.
[0062] The slurry for thermal spraying can be prepared by mixing
spray particles with the above dispersion medium and dispersing the
mixture. For the dispersion, a mixer, a disperser, and the like
including a homogenizer and a blade type stirrer can be used.
[0063] The slurry for thermal spraying disclosed here may further
contain a dispersant as needed. Here, the dispersant is generally a
compound capable of improving the dispersion stability of spray
particles in a dispersion medium in the slurry for thermal
spraying. Such a dispersant can be a compound that essentially
affects spray particles or can be a compound that affects a
dispersion medium, for example. The dispersant can also be a
compound that affects spray particles or a dispersion medium to
improve the surface wettability of the spray particles, a compound
that deflocculates spray particles, or a compound that suppresses
or prevents re-agglomeration of deflocculated spray particles, for
example.
[0064] The dispersant can be appropriately selected from aqueous
dispersants and nonaqueous dispersants according to the above
dispersion medium, and used. Such a dispersant may be any of
polymer dispersants (including polymer surfactant-type
dispersants), surfactant-type dispersants (also called low
molecular dispersants), and inorganic dispersants, and these
dispersants may be any of anionic dispersants, cationic
dispersants, and nonionic dispersants. In other words, the
dispersant can have at least one functional group of anionic
groups, cationic groups, and nonionic groups in the molecular
structure thereof.
[0065] Examples of the aqueous polymer dispersant include
dispersants including polycarboxylic acid compounds such as sodium
polycarboxylate, ammonium polycarboxylate, and polycarboxylic acid
polymers; dispersants including sulfonic acid compounds such as
sodium polystyrene sulfonate, ammonium polystyrene sulfonate,
sodium polyisoprene sulfonate, ammonium polyisoprene sulfonate,
sodium naphthalenesulfonate, ammonium naphthalenesulfonate, sodium
salts of naphthalenesulfonic acid formalin condensates, and
ammonium salts of naphthalenesulfonic acid formalin condensates;
and dispersants including polyethylene glycol compounds. Examples
of the nonaqueous polymer dispersant include dispersants including
acrylic compounds such as polyacrylates, polymethacrylates,
polyacrylamide, and polymethacrylamide; dispersants including
polycarboxylic acid partial alkyl ester compounds that are
polycarboxylic acids partially having alkyl ester bonds;
dispersants including polyalkyl ether compounds such as
polyoxyalkylene alkyl ethers prepared by addition polymerization of
an aliphatic higher alcohol with ethylene oxide; and dispersants
including polyalkylene polyamine compounds.
[0066] As apparent from the description, for example, the concept
of "polycarboxylic acid compounds" in the present description
encompasses the polycarboxylic acid compounds and salts thereof.
The same applies to the other compounds. A compound classified into
one of the aqueous dispersant and the nonaqueous dispersant for
convenience can be used as the other of the nonaqueous dispersant
and the aqueous dispersant depending on the detailed chemical
structure or the usage conditions thereof.
[0067] Examples of the aqueous surfactant-type dispersant (also
called low molecular dispersant) include dispersants including
alkylsulfonic acid compounds, dispersants including quaternary
ammonium compounds, and dispersants including alkylene oxide
compounds. Examples of the nonaqueous surfactant-type dispersant
include dispersants including polyhydric alcohol ester compounds,
dispersants including alkyl polyamine compounds, and dispersants
including imidazoline compounds such as alkyl imidazolines.
[0068] Examples of the aqueous inorganic dispersant include
phosphates such as orthophosphates, metaphosphates, polyphosphates,
pyrophosphates, tripolyphosphates, hexametaphosphates, and organic
phosphates; iron salts such as ferric sulfate, ferrous sulfate,
ferric chloride, and ferrous chloride; aluminum salts such as
aluminum sulfate, polyaluminum chloride, and sodium aluminate; and
calcium salts such as calcium sulfate, calcium hydroxide, and
dibasic calcium phosphate.
[0069] The above dispersants may be used singly or in combination
of two or more of them. In the technique disclosed here, an alkyl
imidazoline compound-containing dispersant and a dispersant
including a polyacrylic acid compound are preferably used in
combination as a specific example. The content of the dispersant
varies with the composition (physical properties) and the like of
spray particles, and thus is not necessarily limited, but is
typically, roughly within a range from 0.01 to 10% by mass where
the mass of spray particles is 100% by mass.
[0070] (Other Optional Components)
[0071] The slurry for thermal spraying may further contain a
viscosity modifier as needed. Here, the viscosity modifier is a
compound capable of reducing or increasing the viscosity of a
slurry for thermal spraying. By appropriately adjusting the
viscosity of a slurry for thermal spraying, a reduction in the
feeding performance of the slurry for thermal spraying can be
suppressed even when the content of spray particles in the slurry
for thermal spraying is comparatively high. Examples of the
compound usable as the viscosity modifier include nonionic polymers
including polyethers such as polyethylene glycol, polyvinyl
alcohol, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl
benzyltrimethylammonium chloride, aqueous urethane resins, gum
arabic, chitosan, cellulose, crystalline cellulose,
methylcellulose, ethylcellulose, hydroxyethylcellulose,
carboxymethylcellulose, carboxymethylcellulose ammonium,
carboxymethylcellulose, carboxyvinyl polymers, lignin sulfonate,
and starch. The content of the viscosity modifier can be within a
range from 0.01 to 10% by mass where the mass of spray particles is
100% by mass.
[0072] The slurry for thermal spraying may further contain an
agglomerating agent (also called a redispersibility improvement
agent or a caking inhibitor, for example) as needed. Here, the
agglomerating agent is a compound capable of agglomerating spray
particles in the slurry for thermal spraying. Typically, the
agglomerating agent is a compound capable of flocculating spray
particles in the slurry for thermal spraying. Depending on physical
properties of spray particles, when the slurry for thermal spraying
contains an agglomerating agent (including a redispersibility
improvement agent, a caking inhibitor, and the like), spray
particles precipitate while the agglomerating agent is interposed
between the spray particles, thus the spray particles that have
precipitated are prevented from aggregating, and the
redispersibility is improved. In other words, even when spray
particles precipitate, the respective particles are prevented from
densely agglomerating (or aggregating) (also called caking or
hard-caking). Hence, when a slurry is transferred to a thermal
spraying apparatus or the like, a turbulent flow is generated in a
slurry, and comparatively easily redisperses precipitates. Thus,
sedimentation during transfer is suppressed, and the feeding
performance to a thermal spraying apparatus is improved. In
addition, when a slurry for thermal spraying is stored in a
container for a long time and spray particles precipitate due to
long time standing, the spray particles can be redispersed by a
simple shaking operation such as vertical shaking of a container by
hand, for example. Hence, the feeding performance to a thermal
spraying apparatus is improved.
[0073] The agglomerating agent or the redispersibility improvement
agent may be any of aluminum-containing compounds, iron-containing
compounds, phosphoric acid-containing compounds, and organic
compounds. Examples of the aluminum-containing compound include
aluminum sulfate, aluminum chloride, and polyaluminum chloride
(also called PAC and PAC1). Examples of the iron-containing
compound include ferric chloride and polyferric sulfate. Examples
of the phosphoric acid-containing compound include sodium
pyrophosphate. The organic compound may be any of anionic
compounds, cationic compounds, and nonionic compounds, and is
exemplified by organic acids such as malic acid, succinic acid,
citric acid, maleic acid, and maleic anhydride,
diallyldimethylammonium chloride polymers, lauryltrimethylammonium
chloride, naphthalenesulfonic acid condensates, sodium
triisopropylnaphthalenesulfonate, sodium polystyrene sulfonate,
isobutylene-maleic acid copolymers, and carboxyvinyl polymers.
[0074] The slurry for thermal spraying may further contain an
antifoaming agent as needed. Here, the antifoaming agent is a
compound capable of preventing foam from generating in a slurry for
thermal spraying at the time of production of a slurry for thermal
spraying or thermal spraying or is a compound capable of
eliminating foam generated in a slurry for thermal spraying.
Examples of the antifoaming agent include silicone oil, silicone
emulsion antifoaming agents, polyether antifoaming agents, and
fatty acid ester antifoaming agents.
[0075] The slurry for thermal spraying may further contain
additives such as antiseptics or fungicides and antifreezing agents
as needed. Examples of the antiseptic or the fungicide include
isothiazoline compounds, azole compounds, and propylene glycol.
Examples of the antifreezing agent include polyhydric alcohols such
as ethylene glycol, diethylene glycol, propylene glycol, and
glycerol.
[0076] When the above additives such as the agglomerating agent,
the viscosity modifier, the antifoaming agent, the antiseptic, and
the fungicide is used, any one of them can be used, or two or more
of them can be used in combination. The total content of these
additives can be roughly within a range from 0.01 to 10% by mass
where the mass of spray particles is 100% by mass.
[0077] When additives such as a dispersant, a viscosity modifier,
an agglomerating agent, a redispersibility improvement agent, an
antifoaming agent, an antifreezing agent, an antiseptic, and a
fungicide are used as optional components, such an additive can be
added to a dispersion medium concurrently with spray particles or
can be added separately at any timing, at the time of the
preparation of the slurry for thermal spraying.
[0078] The above compounds exemplified as various additives can
exhibit functions as other additives in addition to a principal
purpose thereof. In other words, for example, a compound of the
same type or a compound having the same composition can exhibit
functions as two or more additives.
[0079] The slurry for thermal spraying prepared in this manner can
be so prepared as to have a feeding performance index If of 70% or
more, which is determined in accordance with the following
procedure (1) to (3).
[0080] <Calculation of Feeding Performance Index If>
[0081] (1) Spray particles contained in 800 mL of a slurry for
thermal spraying are weighed to give A kg.
[0082] (2) Through a tube that has an inner diameter of 5 mm and a
length of 5 m and is placed horizontally, 800 mL of the slurry for
thermal spraying in which the spray particles are in a dispersion
state is allowed to flow at a flow rate of 35 mL/min, and the
slurry is recovered. The spray particles contained in the recovered
slurry are weighed to give B kg.
[0083] (3) Based on A and B, a value is calculated in accordance
with the equation: If (%)=B/A.times.100 as the feeding performance
index If.
[0084] The feeding performance index is an index capable of
evaluating the feeding performance of spray particles in a slurry
for thermal spraying to a thermal spraying apparatus. By specifying
the feeding performance index If of 800 mL of a slurry for thermal
spraying, the feeding performance of a slurry for thermal spraying
usable in various thermal spraying conditions (for example, larger
scale thermal spraying conditions) can be more appropriately
evaluated. In addition, by increasing the feeding performance index
value, the absolute value of the zeta potential in a slurry for
thermal spraying can be allowed to approach to a favorable value
(for example, 0 mV). Consequently, various design standards for a
slurry for thermal spraying that can be subjected to satisfactory
thermal spraying in various thermal spraying conditions can be
obtained.
[0085] By specifying the feeding rate to a flow rate of 35 mL/min,
a turbulent flow can be generated in a slurry for thermal spraying
flowing through a tube having the above dimensions. By generating
such a turbulent flow, the feeding performance of a slurry can be
evaluated while the extrusion force of the slurry and the
dispersibility of the spray particles are increased. The material
of the tube used for the evaluation of the feeding performance is
not strictly limited, but in order to achieve smooth feeding
conditions of a slurry for thermal spraying, a tube made from a
flexible resin such as polyurethane, polyvinyl chloride, and
polytetrafluoroethylene is preferably used. In order to observe
spray particles flowing in a tube from outside, a transparent or
translucent tube can also be used.
[0086] In the technique disclosed here, when the feeding
performance index If is 70% or more, the feeding performance of
spray particles to a thermal spraying apparatus is determined to be
sufficient. The feeding performance index If is preferably 75% or
more, more preferably 80% or more, even more preferably 85% or
more, and, for example, further preferably 90% or more (ideally,
100%). In a slurry for thermal spraying satisfying such a feeding
performance index, spray particles are prevented from sedimenting
when the slurry is fed to a thermal spraying apparatus, and
accordingly, a larger amount of spray particles can be fed to a
thermal spraying apparatus. In addition, the slurry concentration
is unlikely to differ between immediately after the start of
feeding of a slurry for thermal spraying and the end of the
feeding. This allows spray particles to be stably fed to a thermal
spraying apparatus at high efficiency, and a high quality sprayed
coating can be formed. p In such a slurry for thermal spraying, the
proportion of spray particles is not limited to particular values.
For example, the proportion of spray particles in the whole slurry
for thermal spraying is preferably 10% by mass or more, more
preferably 15% by mass or more, and can be, for example, 20% by
mass or more. When the solid content concentration is 10% by mass
or more, the thickness of a sprayed coating produced from the
slurry for thermal spraying per unit time can be increased. In
other words, the thermal spraying efficiency can be improved.
[0087] In the slurry for thermal spraying, the proportion of spray
particles can be 70% by mass or less, preferably 65% by mass or
less, and, for example, 50% by mass or less. When the solid content
concentration is 70% by mass or less, flowability suited for
feeding a slurry for thermal spraying to a thermal spraying
apparatus can be achieved.
[0088] The viscosity of the slurry for thermal spraying can be, but
is not necessarily limited to, 1,000 mPas or less, preferably 500
mPas or less, more preferably 100 mPas or less, and, for example,
50 mPas or less. When the slurry for thermal spraying have a lower
viscosity, the flowability can be further improved. The lower limit
of the viscosity of the slurry for thermal spraying is not limited
to particular values, but a slurry for thermal spraying having a
lower viscosity can mean a lower proportion of particles for
thermal spraying. From such a viewpoint, the viscosity of the
slurry for thermal spraying is, for example, preferably 0.1 mPas or
more, more preferably 5 mPas or more, and even more preferably 10
mPas or more. By adjusting the viscosity of a slurry for thermal
spraying within the above range, the feeding performance index can
be adjusted to a preferred range.
[0089] The pH of the slurry for thermal spraying is not limited to
particular values, but is preferably 2 or more and 12 or less. In
terms of easy handling of the slurry for thermal spraying, the pH
is preferably 6 or more and 8 or less. For example, in order to
control the zeta potential of spray particles, the pH may be a
value out of a range of 6 or more and 8 or less, and may be 7 or
more and 11 or less, or 3 or more and 7 or less, for example.
[0090] The pH of the slurry for thermal spraying can be controlled
by known various acids, bases, or salts thereof. Specifically,
organic acids such as carboxylic acid, organic phosphonic acids,
and organic sulfonic acids; inorganic acids such as phosphoric
acid, phosphorous acid, sulfuric acid, nitric acid, hydrochloric
acid, boric acid, and carbonic acid; organic bases such as
tetramethylammonium hydroxide, trimethanolamine, and
monoethanolamine; inorganic bases such as potassium hydroxide,
sodium hydroxide, and ammonia; and salts thereof are preferably
used.
[0091] The pH of a slurry for thermal spraying can be a value
determined. by using a glass electrode pH meter (for example,
manufactured by Horiba, Ltd., Benchtop pH meter (F-72)) with
authentic pH standard solutions (for example, a phthalate pH
standard solution (pH: 4.005/25.degree. C.), a neutral phosphate pH
standard solution (pH: 6.865/25.degree. C.), and a carbonate pH
standard solution (pH: 10.012/25.degree. C.)) in accordance with
JIS Z8802:2011.
[0092] In the slurry for thermal spraying, spray particles
preferably form secondary particles. By controlling the amount and
the average particle size of secondary particles including spray
particles, the zeta potential can be controlled. Whether spray
particles form secondary particles can be estimated by measuring
the average particle size of spray particles in a slurry and
comparing the value with the average particle size of spray
particles (dry powder) prepared for a slurry for thermal spraying.
For example, when the average particle size after the preparation
of a slurry is 1.2 or more times (more preferably 1.5 or more
times) larger than that before the preparation, it can be
determined that almost all the spray particles form secondary
particles. In contrast, when the average particle size after the
preparation of a slurry is less than 1.2 times larger than that
before the preparation and is not greatly changed, it can be
determined that the spray particles are prevented from forming
secondary particles. The average particle size of spray particles
in a slurry is, for example, a 50% cumulative particle size
(D.sub.50) in volumetric particle size distribution measured by
using a laser diffraction/scattering particle size distribution
analyzer (manufactured by Horiba, Ltd., LA-950). By calculating a
3% cumulative particle size (D.sub.3) and a 97% cumulative particle
size (D.sub.97) in volumetric particle size distribution of spray
particles concurrently with the measurement of the average particle
size, a variation in average particle size (formation condition of
secondary particles) can be estimated. The average particle size of
the secondary particles formed from spray particles in a slurry for
thermal spraying is preferably 30 .mu.m or less, more preferably 25
.mu.m or less, and even more preferably 15 .mu.m or less. The
increase degree of the average particle size of secondary particles
of spray particles in a slurry for thermal spraying relative to the
primary particle size of the spray particles before the preparation
of the slurry for thermal spraying can also be determined. For
example, the average particle size of secondary particles formed
from spray particles in a slurry for thermal spraying is preferably
1.2 or more times larger than the primary particle size of the
spray particles before the preparation of the slurry for thermal
spraying.
[0093] [Materials for Preparation of slurry For Thermal
Spraying]
[0094] As described above, the slurry for thermal spraying
disclosed here can surely achieve good redispersibility by a
treatment such as second shaking even when particles for thermal
spraying precipitate. Hence, for example, the slurry for thermal
spraying in which particles for thermal spraying have precipitated
can be divided into a portion that does not contain the particles
for thermal spraying or contains the particles in a smaller amount
(typically, a supernatant liquid portion) and a portion that
contains all the particles for thermal spraying or contains the
particles in a larger amount (typically, a remainder portion after
removal of the supernatant liquid portion). The portions can be
appropriately mixed and stirred, for example, to give the above
slurry for thermal spraying. Alternatively, the components of the
slurry for thermal spraying can be separately prepared as some
component portions, and then the portions can be appropriately
mixed and stirred, for example, to give the above slurry for
thermal spraying. Thus, the slurry for thermal spraying can also be
prepared in the following manner: the respective components
constituting the slurry for thermal spraying are stored in separate
containers each containing a single component or a mixture of two
or more components, and the components are mixed before thermal
spraying.
[0095] From such a viewpoint, the technique disclosed here provides
a material for preparing a slurry for thermal spraying used for
preparing the slurry for thermal spraying. The preparation material
includes at least one or more of the components constituting the
above slurry for thermal spraying.
[0096] In addition, the material is so constituted as to satisfy a
feeding performance index If of 70% or more when all the components
that constitute a slurry for thermal spraying and include the
preparation material are mixed to prepare a mixed liquid.
[0097] The preparation material may be only some of the components
constituting a slurry for thermal spraying. The preparation
material may be so constituted as to give a slurry for thermal
spraying containing all the components by combining a preparation
material A with another preparation material B or with two or more
preparation materials B, C, etc. As the components constituting a
slurry for thermal spraying, the above optional components
(additives) such as a dispersant and a viscosity modifier can be
included, for example, in addition to the spray particles and the
dispersion medium. Hence, the combination of such a preparation
material is specifically exemplified by the following
constitutions.
EXAMPLE 1
[0098] Preparation material A1: particles for thermal spraying
[0099] Preparation material B1: a dispersion medium
EXAMPLE 2
[0100] Preparation material A2: particles for thermal spraying and
some of a dispersion medium
[0101] Preparation material B2: the remainder of the dispersion
medium
EXAMPLE 3
[0102] Preparation material A3: particles for thermal spraying
[0103] Preparation material B3: a dispersion medium and optional
components (additives)
EXAMPLE 4
[0104] Preparation material A4: particles for thermal spraying
[0105] Preparation material B4: a dispersion medium
[0106] Preparation material C4: optional components (additives)
[0107] When a plurality of optional components are used here, the
preparation material C4 may include preparation materials C4n (n is
natural numbers) of the respective optional components, for
example.
[0108] In this manner, in the material for preparing a slurry for
thermal spraying disclosed here, the respective components
constituting a slurry for thermal spraying, such as spray
particles, a dispersion medium, a dispersant, and other optional
components, may be provided in separate packages each containing a
single component or a mixture of two or more components. The
material for preparing a slurry for thermal spraying may be mixed
with other components (optionally other materials for preparing a
slurry for thermal spraying) before thermal spraying to give a
slurry for thermal spraying. From the viewpoint of easy
transportation, it is preferred that components other than a
dispersion medium be prepared in a single package as a material for
preparing a slurry for thermal spraying, and the dispersion medium
be prepared in another package as a material for preparing a slurry
for thermal spraying (optionally another material for preparing a
slurry for thermal spraying). Components other than the dispersion
medium (particles for thermal spraying and optional components such
as additives) can be in a powder (solid) form, for example. For
example, when the dispersion medium is an easy available material
such as water, a user of the slurry for thermal spraying can
independently prepare such a dispersion medium. In terms of
uniformity of a slurry for thermal spraying or stable performance
of a coating, the slurry for thermal spraying to be subjected to
thermal spraying is preferably prepared as a high concentration
slurry containing spray particles at a higher concentration.
[0109] The above material for preparing a slurry for thermal
spraying may include information for preparing a slurry for thermal
spraying. The information can also be understood as the preparation
method for preparing a slurry for thermal spraying by using the
material for preparing a slurry for thermal spraying. For example,
information about the procedure of mixing components in separate
packages or about materials required in addition to the material
for preparing a slurry for thermal spraying is displayed. Although
the material for preparing a slurry for thermal spraying is so
constructed as to give a feeding performance index If of 70% or
more, information for further improving the If value may be
displayed. Such information may be displayed on the containers of
components or on a covering material or the like in which such a
container is stored. Alternatively, a paper sheet or the like on
which information is described may be set (packed) in the container
of a component. The information can be so constructed as to be
available by a user having the material for preparing a slurry for
thermal spraying through the Internet or the like. Accordingly, the
material for preparing a slurry for thermal spraying disclosed here
can be used to more easily and certainly form a sprayed coating at
high efficiency.
[0110] [Coating Formation Method]
[0111] (Substrate)
[0112] In the method for forming a sprayed coating disclosed here,
the substrate on which a sprayed coating is formed is not limited
to particular substrates. For example, any substrate made from
various materials can be used as long as the substrate is made from
a material that can have an intended resistance when the substrate
is subjected to the thermal spraying. Examples of such a material
include various metals and alloys. Such a material is specifically
exemplified by aluminum, aluminum alloys, iron, steel, copper,
copper alloys, nickel, nickel alloys, gold, silver, bismuth,
manganese, zinc, and zinc alloys. Of them, substrates made of
steels typified by various SUS materials having comparatively high
thermal expansion coefficients in general purpose metal materials
(optionally what is called stainless steel), heat-resistant alloys
typified by inconel, low-expansion alloys typified by invar and
kovar, corrosion-resistant alloys typified by hastelloy, and
aluminum alloys typified by 1,000 series to 7,000 series aluminum
alloys that are useful as lightweight structural materials and the
like are exemplified.
[0113] (Coating Formation Method)
[0114] The slurry for thermal spraying disclosed here can be
subjected to a thermal spraying apparatus based on a known thermal
spraying method and thus can be used as the material for thermal
spraying in order to form a sprayed coating. When the slurry for
thermal spraying is allowed to stand for a certain period of time
typically for storage, the spray particles can start to sediment
and precipitate in a dispersion medium. Hence, the slurry for
thermal spraying in the technique disclosed here can be so prepared
as to give a feeding performance index If of 70% or more, which is
determined by the above procedure, when the slurry is subjected to
thermal spraying (for example, in the preparation step for feeding
the slurry to a thermal spraying apparatus). For example, a slurry
for thermal spraying in a storage state before thermal spraying
(also called a precursor liquid) can be prepared as a high
concentration slurry containing spray particles at a higher
concentration.
[0115] As the thermal spray method of appropriately, thermally
spraying the slurry for thermal spraying, a thermal spray method
such as plasma spraying and high velocity flame spraying can be
preferably adopted, for example.
[0116] The plasma spraying is a thermal spray method that uses a
plasma flame as a thermal spraying heat source for softening or
melting a thermal spraying material. Between electrodes, arc is
generated, and the arc functions to convert a working gas into
plasma. Such a plasma flow is ejected from a nozzle as a plasma jet
at high temperature and high speed. The plasma spraying generally
encompasses coating techniques in which a material for thermal
spraying is introduced to the plasma jet, then heated and
accelerated, and deposited on a substrate to form a sprayed
coating. The plasma spraying can be atmospheric plasma spraying
(APS) that is performed in the atmosphere, low pressure plasma
spraying (LPS) in which thermal spraying is performed at a lower
pressure than the atmospheric pressure, or high pressure plasma
spraying in which plasma spraying is performed in a pressurized
container at a higher pressure than the atmospheric pressure, for
example. In such plasma spraying, by using a plasma jet at about
5,000.degree. C. to 10,000.degree. C. to melt and accelerate a
thermal spraying material, the spray particles can be hit against a
substrate at a speed of about 300 m/s to 600 m/s and deposited, for
example.
[0117] The high velocity flame spraying can be high velocity oxygen
fuel (HVOF) thermal spraying, warm spray thermal spraying, or high
velocity air fuel (HVAF) flame spraying, for example.
[0118] The HVOF thermal spraying is a flame spraying that uses a
combustion flame prepared by burning a mixture of a fuel and oxygen
at high pressure, as the heat source for thermal spraying. By
increasing the pressure in a combustion chamber, a continuous
combustion flame is ejected from a nozzle at high speed (optionally
supersonic speed) as a high temperature gas flow. The HVOF thermal
spraying generally encompasses coating techniques in which a
material for thermal spraying is introduced to the gas flow, then
heated and accelerated, and deposited on a substrate to form a
sprayed coating. In the HVOF thermal spraying, for example, by
feeding a slurry for thermal spraying to a supersonic combustion
flame jet at 2,000.degree. C. to 3,000.degree. C., a dispersion
medium can be removed (optionally burned or evaporated,
hereinafter, the same applies) from the slurry. Concurrently, the
spray particles can be softened and melted, then hit against a
substrate at a high speed of 500 m/s to 1,000 m/s, and deposited.
The fuel used for the high velocity flame spraying may be a
hydrocarbon gas fuel such as acetylene, ethylene, propane, and
propylene or may be a liquid fuel such as kerosene and ethanol. As
a thermal spraying material has a higher melting point, the
temperature of the supersonic combustion flame is preferably
higher. From this viewpoint, a gas fuel is preferably used.
[0119] Alternatively, a thermal spraying method called warm spray
thermal spraying to which the HVOF thermal spraying is applied can
be adopted. The warm spray thermal spraying is typically a
technique in which thermal spraying is performed in a condition
where the combustion flame in the HVOF thermal spraying is mixed
with a cooling gas including nitrogen or the like at around room
temperature to reduce the temperature of the combustion flame,
thereby forming a sprayed coating. The thermal spraying material
when subjected to thermal spraying is not necessarily, completely
melted, but may be partially melted or may be in a softened state
at a temperature not higher than the melting point thereof, for
example. In the warm spray thermal spraying, for example, by
feeding a slurry for thermal spraying to a supersonic combustion
flame jet at 1,000.degree. C. to 2,000.degree. C., a dispersion
medium can be removed (optionally burned or evaporated,
hereinafter, the same applies) from the slurry. Concurrently, the
spray particles can be softened and melted, then hit against a
substrate at a high speed of 500 m/s to 1,000 m/s, and
deposited.
[0120] The HVAF thermal spraying is a thermal spraying method in
which air is fed in place of oxygen as a combustion support gas in
the HVOF thermal spraying. By the HVAF thermal spraying, the
thermal spraying temperature can be lowered as compared with the
HVOF thermal spraying. For example, by feeding a slurry for thermal
spraying to a supersonic combustion flame jet at 1,600.degree. C.
to 2,000.degree. C., a dispersion medium can be removed (optionally
burned or evaporated, hereinafter, the same applies) from the
slurry. Concurrently, the spray particles can be softened and
melted, then the spray particles can be hit against a substrate at
a high speed of 500 m/s to 1,000 m/s, and can be deposited.
[0121] In the invention disclosed here, when the slurry for thermal
spraying is preferably subjected to high velocity flame spraying or
plasma spraying because a material for thermal spraying even having
a comparatively large particle size can be sufficiently softened
and melted, a slurry for thermal spraying including spray particles
even at a high content can be thermally sprayed with good
flowability, and a dense sprayed coating can be efficiently
formed.
[0122] Although not critical, the slurry for thermal spraying is
fed to a thermal spraying apparatus preferably at a flow rate of 10
mL/min or more and 200 mL/min or less. When the slurry for thermal
spraying is fed at a rate of about 10 mL/min or more, the slurry
that is flowing in a device for feeding a slurry for thermal
spraying (for example, a slurry feed tube) can be made in a
turbulent flow state, and the extrusion force of the slurry can be
increased. In addition, the spray particles can be prevented from
sedimenting. Such a condition is thus preferred. From such a
viewpoint, the flow rate when the slurry for thermal spraying is
fed is preferably 20 mL/min or more and more preferably 30 mL/min
or more. Meanwhile, when the feeding rate is excessively high, the
amount of the slurry may exceed the amount of a slurry that can be
thermally sprayed from a thermal spraying apparatus, and thus such
a condition is unfavorable. From such a viewpoint, the flow rate
when the slurry for thermal spraying is fed is appropriately 200
mL/min or less, preferably 150 mL/min or less, and more preferably
100 mL/min or less, for example.
[0123] The slurry for thermal spraying is fed to a thermal spraying
apparatus preferably by an axial feed system. In other words, the
slurry for thermal spraying is fed preferably in the same direction
as the axis of a jet flow generated in a thermal spraying
apparatus. For example, when the slurry for thermal spraying of the
present invention in a slurry state is fed by the axial feed system
to a thermal spraying apparatus, the thermal spraying material in
the slurry for thermal spraying is unlikely to adhere to the inside
of the thermal spraying apparatus because the slurry for thermal
spraying has good flowability. Consequently, a dense sprayed
coating can be efficiently formed. Such a condition is thus
preferred.
[0124] When a common feeder is used to feed the slurry for thermal
spraying to a thermal spraying apparatus, the feed amount varies
periodically, and thus stable feeding may be difficult. When the
feed amount of the slurry for thermal spraying oscillates due to
the periodic variation of the feed amount, the thermal spraying
material is unlikely to be uniformly heated in a thermal spraying
apparatus, and an uneven sprayed coating can be formed in some
cases. In order to stably feed the slurry for thermal spraying to a
thermal spraying apparatus, a two-stroke system, or two feeders may
be used in such a manner that variable periods of the feed amounts
of the slurry for thermal spraying from both the feeders have
opposite phases to each other. Specifically, the feeding system can
be controlled to give such periods that when the feed amount of one
feeder increases, the feed amount of the other feeder decreases,
for example. When the slurry for thermal spraying of the present
invention is fed to a thermal spraying apparatus by the two-stroke
system, a dense sprayed coating can be efficiently formed because
the slurry for thermal spraying has good flowability.
[0125] As the means for stably feeding a material for thermal
spraying in a slurry form to a thermal spraying apparatus, the
slurry sent from a feeder may be once stored in a storage tank
provided just before the thermal spraying apparatus, and the slurry
may be fed from the storage tank to the thermal spraying apparatus
by using natural drop. Alternatively, the slurry in the tank may be
forcedly fed to the thermal spraying apparatus by using a means
such as a pump. When the slurry is forcedly fed by a means such as
a pump, a thermal spraying material in the slurry is unlikely to
adhere to the inside of a tube that connects the tank and the
thermal spraying apparatus. Such a condition is thus preferred. In
order to uniformize the distribution state of components in the
slurry for thermal spraying in the tank, a means of stirring the
slurry for thermal spraying in the tank may be provided.
[0126] The slurry for thermal spraying is fed to a thermal spraying
apparatus preferably through a metal conductive tube, for example.
When a conductive tube is used, static electricity can be prevented
from generating, and thus the feed amount of the slurry for thermal
spraying is unlikely to vary. The inner surface of the conductive
tube preferably has a surface roughness Ra of 0.2 .mu.m or
less.
[0127] A thermal spraying distance is the distance from the tip of
a nozzle of a thermal spraying apparatus to a substrate and is
preferably set to 30 mm or more. When the thermal spraying distance
is excessively small, the time for removing a dispersion medium in
the slurry for thermal spraying or for softening/melting spray
particles may be insufficiently secured, or a thermal spraying heat
source is excessively close to a substrate, and thus the substrate
may deteriorate or be deformed. Such a condition is therefore
unfavorable.
[0128] The thermal spraying distance is preferably about 200 mm or
less (preferably 150 mm or less, for example, 100 mm or less). Such
a distance allows spray particles sufficiently heated to reach to a
substrate while the temperature is maintained, and thus a denser
sprayed coating can be produced.
[0129] For thermal spraying, a substrate is cooled preferably from
the side opposite to the side undergoing thermal spraying. Such
cooling can be water cooling or cooling with an appropriate
refrigerant.
[0130] (Sprayed Coating)
[0131] By the technique disclosed here, a sprayed coating including
a compound having the same composition as spray particles and/or a
degradation product thereof is formed.
[0132] The sprayed coating is formed by using a slurry for thermal
spraying in which spray particles have an absolute zeta potential
of 200 mV or less and are satisfactory dispersed. Thus, spray
particles are maintained in an appropriate dispersion state and a
flow state in the slurry for thermal spraying, are stably fed to a
thermal spraying apparatus, and form a uniform sprayed coating. The
spray particles are not hit by a flame or a jet but can be
efficiently fed to the vicinity of the center of a heat source and
sufficiently softened or melted. Hence, the softened or melted
spray particles densely adhere to a substrate and to each other
with good adhesiveness. Accordingly, a sprayed coating having good
uniformity and adhesiveness is formed at an appropriate coating
forming speed.
[0133] Some examples of the present invention will next be
described, but the present invention is not intended to be limited
to these examples.
[0134] [Preparation of Slurry for Thermal Spraying]
[0135] As spray particles, yttria (Y.sub.2O.sub.3), alumina
(Al.sub.2O.sub.3), yttrium fluoride (YF.sub.3), and yttrium
oxyfluorides having various compositions (YOF,
Y.sub.5O.sub.4F.sub.7, Y.sub.6O.sub.5F.sub.8,
Y.sub.7O.sub.6F.sub.9) , having the corresponding average particle
sizes shown in Table 1 were prepared. As dispersion media,
distilled water was prepared as an aqueous dispersion medium, and a
mixed solvent containing ethanol (EtOH), isopropyl alcohol
(i-PrOH), and n-propyl alcohol (n-PrOH) at 85:5:10 in terms of
volume ratio was prepared as a nonaqueous dispersion medium. As
additives as optional components, dispersants and a viscosity
modifier were prepared. As the dispersant, any of an aqueous
nonionic surfactant-type dispersant (manufactured by Dai-ichi Kogyo
Seiyaku Co., Ltd., Noigen XL-400) and a nonaqueous special
polycarboxylic acid polymer surfactant (manufactured by Kao
Corporation, HOMOGENOL L-18) was used. As the viscosity modifier,
an anionic special modified polyvinyl alcohol (PVOH) (manufactured
by The Nippon Synthetic Chemical Industry Co., Ltd., Gohsenx
L-3266) was used. Such particles for thermal spraying and a
dispersion medium were prepared in different containers in such a
manner that the proportion of particles for thermal spraying would
be 30% by mass.
[0136] The particles for thermal spraying and the dispersion medium
were mixed together with a dispersant and a viscosity modifier in
accordance with the formulations shown in Table 1, giving slurries
for thermal spraying of Examples 1 to 27 each having a proportion
of particles for thermal spraying of 30% by mass. In the present
embodiment, the amount of the viscosity modifier was constant at
0.1% by mass relative to the mass of spray particles. In Table 1,
"-" in the viscosity modifier column means that no viscosity
modifier was used. The amount of a dispersant was appropriately
controlled while the dispersion state of spray particles in a
slurry for thermal spraying was observed, and the amounts used are
indicated in the "content" column in Table 1.
[0137] [Presence or Absence of Secondary Particles Formed]
[0138] The average particle size of the spray particles in each
slurry for thermal spraying prepared was determined by using a
laser diffraction/scattering particle size distribution analyzer
(manufactured by Horiba, Ltd., LA-950). The average particle size
of the spray particles in the slurry was compared with the average
primary particle size of spray particles prepared for the slurry
for thermal spraying. When the average particle size of the spray
particles in the slurry was 1.5 or more times larger, it was
determined that the spray particles agglomerate to form secondary
particles in the slurry. An example in which spray particles are
determined to form secondary particles is indicated by "presence"
in the secondary particle formation column in Table 1, and an
example in which spray particles are determined not to form
secondary particles is indicated by "absence".
[0139] [Viscosity]
[0140] The viscosity of each slurry for thermal spraying prepared
was determined by using a viscometer (manufactured by Rion,
Viscotester VT-03F) in a room temperature (25.degree. C.)
environment at a rotation speed of 62.5 rpm. The results are shown
in Table 1.
[0141] [Zeta Potential]
[0142] The zeta potential of the spray particles in each slurry for
thermal spraying prepared was determined by using an ultrasonic
particle size distribution/zeta potential analyzer (manufactured by
Dispersion Technology, DT-1200).
[0143] [Feeding Performance Index If]
[0144] The feeding performance index If of each slurry for thermal
spraying prepared was determined by the following procedure. In
other words, first, a polyurethane tube (manufactured by CHIYODA,
Touch Tube (urethane) TE-8 with an outer diameter of 8 mm and an
inner diameter of 5 mm) having an inner diameter of 5 mm and a
length of 5 m was placed on a test table with no difference in
height. To one end of the tube, a roller pump for feeding a slurry
was connected, and to the other end, a slurry recovery container
was connected.
[0145] A prepared slurry for thermal spraying was stirred with a
magnetic stirrer, and good dispersion state of the spray particles
was ascertained. The slurry was then fed into the tube at a flow
rate of 35 mL/min. The slurry for thermal spraying that had passed
through the tube was recovered in the recovery container, and the
spray particles contained in the recovered slurry was weighed to
give mass B. From the previously determined mass A of the spray
particles contained in 800 mL of the slurry for thermal spraying
after preparation and the mass B of the spray particles contained
in the recovered slurry, the feeding performance index If was
calculated in accordance with the following equation, and the
results are shown in Table 1.
If(%)=B/A.times.100
[0146] [Formation of Sprayed Coating]
[0147] Each slurry for thermal spraying prepared above was used and
thermally sprayed by an atmospheric plasma spraying (APS) method to
form a sprayed coating. The thermal spraying conditions were as
shown below.
[0148] In other words, first, a SS400 steel plate (70 mm.times.50
mm.times.2.3 mm) was prepared and was subjected to roughening
treatment, and the product was used as the substrate to be
subjected to thermal spraying. For APS thermal spraying, a
commercially available plasma spraying apparatus (manufactured by
Praxair, SG-100) was used. As for plasma generation conditions, at
atmospheric pressure, argon gas was fed at a pressure of 100 psi,
helium gas was fed at a pressure of 90 psi as plasma working gases,
and the plasma generation power was 40 kW. To feed a slurry for
thermal spraying to a thermal spraying apparatus, a slurry feeder
was used to feed the slurry at a feed amount of about 100 mL/min to
a burner chamber in the thermal spraying apparatus. When the slurry
was fed to the thermal spraying apparatus, a storage tank was
install adjacent to the thermal spraying apparatus, the prepared
slurry for thermal spraying was once stored in the storage tank,
and then the slurry was fed from the storage tank to the thermal
spraying apparatus by using natural drop. A plasma jet was ejected
from a nozzle of the thermal spraying apparatus, and the slurry for
thermal spraying fed to the burner chamber was allowed to fly
together with the jet while the dispersion medium in the slurry was
removed. Concurrently, the spray particles were melted and were
sprayed to a substrate, and consequently a coating was formed on
the substrate. The conveyance speed of a thermal spraying gun was
600 mm/min, and the thermal spraying distance was 50 mm.
[0149] [Coating Formation Efficiency]
[0150] The coating formation efficiency (adhesion efficiency) of
spray particles was evaluated when the slurry for thermal spraying
of each example was thermally sprayed to form a coating.
Specifically, the thickness (.mu.m) of a sprayed coating formed by
a single pass (which means that thermal spraying is performed once
from a thermal spraying apparatus to a substrate) in the above
thermal spraying conditions was determined. In the present
embodiment, when the coating formation efficiency is 2.5 .mu.m or
more by a single pass, the formation efficiency is evaluated as
good. [Table 1]
[0151] As shown in Table 1, it was revealed that the coating
formation efficiency greatly varies as slurries for thermal
spraying have different zeta potentials even when spray particles
have the same composition and the same average particle size and
are contained in the same amount (at the same concentration) as
shown in Examples 1 to 16. It was further revealed that a good
coating formation efficiency of 2.5 .mu.m or more is achieved when
the absolute value of the zeta potential is 200 mV or less. A
higher coating formation efficiency means that a slurry for thermal
spraying fed to a thermal spraying apparatus has good flowability
and good feeding performance.
[0152] It was also revealed that in the slurry for thermal spraying
having good coating formation efficiency, the spray particles form
secondary particles. The result suggests that in the slurry for
thermal spraying disclosed here, primary particles of spray
particles agglomerate to give a certain size, and accordingly the
agglomeration particles (secondary particles) are stably dispersed
in the flowing slurry for thermal spraying. It was ascertained that
as a result, a slurry for thermal spraying having an absolute zeta
potential of 200 mV or less had good feeding performance, which was
indicated by a feeding performance index If of 70% or more.
[0153] Specific examples of the present invention have been
described in detail hereinbefore, but are merely illustrative
examples, and are not intended to limit the scope of claims. The
techniques described in the scope of claims include various
modifications and changes of the above exemplified specific
examples. For example, in the above embodiment, slurries for
thermal spraying were so prepared as to have various zeta
potentials while the types of the dispersant and the viscosity
modifier were fixed. However, selection and use of additives such
as a dispersant and a viscosity modifier suitable for controlling
the zeta potential can be understood by a person skilled in the art
on the basis of teachings disclosed here and common general
knowledge at the time of patent application.
* * * * *